Sintered alloy having wear resistance for valve seat and method for manufacturing the same

ABSTRACT

A sintered alloy having an improved wear resistance and a workability for a valve seat. The alloy contains iron as a main component, carbon, silicon, chromium, molybdenum, cobalt, maganese, lead, vanadium, advantageously boron nitride, and tungsten. The strength, wear resistance, and material properties are improved by a sub-zero treatment. Sintered alloy with wear resistance used for a valve seat comprises Fe as a main component, C of 1.2 to 1.7 wt %, Cr of 3.5 to 5.0 wt %, Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0 wt %, W of 7.0 to 10.0 wt %, Co of 2.0 to 3.5 wt %, boron nitride of 0.1 to 1.0 wt %, S of 0.2 to 0.4 wt %, Mn of 0.2 to 0.5 wt %, advantageously 0.2 to 0.6% Si, and Pb of 10.0 to 15.0 wt %. Sintered alloy for an valve seat is manufactured by a sub-zero treatment so that the amount of metallic particles separated from a base matrix decreases and a size of the separated metallic particle becomes small.

FIELD OF THE INVENTION

[0001] The present invention relates to sintered alloy having anexcellent wear resistance for a valve seat and a method formanufacturing the same. More particularly, the present invention relatesto a sintered lead (Pb) impregnated alloy having an excellent wearresistance for an valve seat, which is produced by a sub-zero treatmentfor a metal power containing iron (Fe) as a main component, carbon (C),optionally silicon (Si), chromium (Cr), molybdenum (Mo), cobalt (Co),maganese (Mn), vanadium (V) and tungsten (W) so that amount of metallicparticles separated from a base matrix decreases and a size of theseparated metallic particle becomes small when an abrasion of thesintered alloy is in process, whereupon a wear resistance and impactresistance are improved and a self-lubricity and a workability isenhanced, and method of manufacturing the same.

BACKGROUND OF THE INVENTION

[0002] A conventional sintered alloy with wear resistance used for avalve seat contains Fe as a main component, C of from 0.4 to 1.0 wt %,Si of 0.1 to 1.0 wt %, Cr of 0.5 to 2.0 wt %, Mo of from 6.0 to 10.0 wt%, Co of from 6.0 to 15.0 wt %, and lead (Pb) of from 6.0 to 18.0 wt %.

[0003] The processes as follows manufacture such a sintered alloy havingan excellent wear resistance used for a valve seat. First of all, themetal powders as above except Pb are mixed and then a surface pressureof from 4 to 8 ton/ cm³ is applied to the mixture of metal power. Undera reducing atmosphere, a preliminary sinter process is performed at atemperature of from 750-800° C. for 40 minutes and a forging process isperformed at a surface pressure of 7 to 10 ton/cm³.

[0004] Thereafter, a main sinter process is performed at a temperaturefrom 1,100 to 1,1400° C. for 30-50 minutes under hydrogen atmosphere andthen Pb is impregnated at a temperature from 400 to 450° C. for 10-30minutes. Then a barrel process is performed at same temperature for80-110 minutes. The sintered alloy, having an excellent wear resistancewhen used for an automobile engine valve seat, is thereby produced.

[0005] However, the sintered alloy having components as described abovehas a microstructure characteristic in which giant metal particles aredispersed in the base matrix. Such giant metal particles cause localweaknesses, and a crack can form when an external impact is applied.Therefore, the impact resistance of the alloy is poor. In turn, the wearresistance will be deteriorated because the metal particles fall awayfrom the abrasive cracked surface. Further, there is problem thatcompressed gas in a cylinder is leaked via these cracks.

[0006] The cost and productivity for producing a conventional sinteredalloy with wear resistance for a valve seat is decreased due to a greatdeal of process steps involved, for example the separate impregnationwith lead, and the impact resistance and wear resistance aredeteriorated by giant particles dispersed within a base matrix.Additionally, a leakage of compressed air can occur. There is arecognized need in the industry for improved alloys for valve seats.

SUMMARY OF THE INVENTION

[0007] The present invention is contrived to solve the foregoingproblems. It is an object of the present invention to provide a sinteredalloy for a valve seat, and also the valve seat made from the sinteredalloy, having an improved wear resistance and a workability. Thesintered alloy contains iron (Fe) as a main component, carbon (C),optionally silicon (Si), chromium (Cr), molybdenum (Mo), cobalt (Co),maganese (Mn), lead (Pb), vanadium (V) and tungsten (W). It is also anobject of this invention to provide a method of manufacturing thesintered alloy and also the valves made from the sintered alloy.

[0008] The present invention provides a sintered alloy with excellentwear resistance used for a valve seat. As used herein, the compositionsof metals except lead are given as the composition in the sinteredalloy, and the composition of lead is given as the amount in thelead-impregnated sintered alloy composition. The impregnated sinteredalloy comprises:

[0009] A) between about 85 parts by weight and a 90 parts by weight, forexample 88 parts by weight, based on 100 parts by weight of thelead-impregnated sintered alloy composition, of a sinterable metalpowder comprising:

[0010] Fe as a main component, comprising for example 63.9% to 85.8% ofthe sintered powder;

[0011] C of 1.2 to 1.7 wt %, for example about 1.4%;

[0012] Cr of 3.5 to 5.0 wt %, for example about 4%;

[0013] Mo of 2.0 to 4.0 wt %, for example about 3%;

[0014] V of 3.0 to 5.0 wt %, for example about 3.5% to about 4%;

[0015] W of 7.0 to 10.0 wt %, for example about 8.5% to about 9%;

[0016] Co of 2.0 to 3.5 wt %, for example about 2.5% to about 3%;

[0017] boron nitride of 0.1 to 1.0 wt %, for example about 0.4% to about0.6%;

[0018] optionally Si of 0.2 to 0.6 wt %, in one embodiment of 0.2 to 0.4wt %, for example about 0.3%;

[0019] S of 0.2 to 0.4 wt %, for example about 0.3%; and

[0020] Mn of 0.2 to 0.5 wt %, for example about 0.3%; and

[0021] B) Pb of 10.0 parts by weight to 15.0 parts by weight, forexample about 12 parts by weight, wherein the PB is impregnated into thesintered metal powder.

[0022] A method for manufacturing the sintered alloy having an excellentwear resistance for a valve comprises;

[0023] mixing 85 parts to about 90 parts by weight of powders of: Fe asa main component, having for example 63.9% to 85.8%, C of 1.2 to 1.7 wt%, Cr of 3.5 to 5.0 wt %, Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0 wt %, Wof 7.0 to 10.0 wt %, Co of 2.0 to 3.5 wt %, boron nitride of 0.1 to 1.0wt %, S of 0.2 to 0.4 wt %, and Mn of 0.2 to 0.5 wt %, and applying asurface pressure of 5 to 8 ton/cm³ to obtain a mixed metal powder;

[0024] sintering the mixed metal powder, advantageously at a temperaturefrom 1,140 to 1,180° C., and then cooling, for example by air or under agas atmosphere, to form a sintered alloy;

[0025] further cooling the sintered alloy and performing a sub-zerotreatment described herein at a temperature from −160 to −200° C.; and

[0026] impregnating at a temperature from 450 to 550° C. thesub-zero-treated sintered alloy with Pb so that the lead content of theimpregnated sintered alloy is from 10.0 to 15.0 wt %; and

[0027] performing a barrel process on the sintered alloy impregnatedwith the Pb at a temperature from 450 to 550° C.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, the sintered alloy according to the preferredembodiment of the present invention will be explained in more detail. Amethod for manufacturing a sintered alloy according to the presentinvention is described in detail by steps hereunder.

[0029] In the alloy of the present invention, Fe is a main component andthe content of each alloy steel component is specified in order toimprove a wear resistance and workability.

[0030] In a first step, Fe as a main component, C of 1.2 to 1.7 wt %, Crof 3.5 to 5.0 wt %, Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0 wt %, W of7.0 to 10.0 wt %, Co of 2.0 to 3.5 wt %, boron nitride of 0.1 to 1.0 wt%, S of 0.2 to 0.4 wt %, Mn of 0.2 to 0.5 wt %, and optionally S of 0.2to 0.4% are mixed and then a surface pressure from 5 to 8 ton/cm³ isapplied.

[0031] The mechanical property of the sintered alloy variessignificantly with a content of C. A content of C is used in the rangefrom 1.2 to 1.7 wt % against the total weight of the composition of thesintered alloy. When the content of C is less than 1.2 wt %, thestrength and hardness are insufficient. Additionally, when the contentof C is more than 1.7 wt %, the tensile strength and a hardness of thesintered alloy again decrease.

[0032] Cr is added in order to increase a wear resistance and a cuttingability. Cr is used in the range from 3.5 to 5.0 wt % against the totalweight of the composition of the sintered alloy. When the content of Cris less than 3.5 wt %, the desired wear resistance and corrosionresistance cannot be obtained. On the other hand, when the content of Cris more than 5.0 wt %, the processability is reduced.

[0033] Mo is added in order to increase a cutting ability, the tensilestrength at a high temperature, and the hardness. Mo is used in therange from 2.0 to 4.0 wt % against the total weight of the compositionof the sintered alloy. When the content of Mo is less or more than theabove range, strength and hardness are not increased.

[0034] V is added in order to adjust a grain. V is used in the rangefrom 3.0 to 5.0 wt % against the total weight of the composition of thesintered alloy. When the content of V is less than 3.0 wt %, wearresistance effect is reduced. When the content of V is more than 5.0 wt%, increased performance is not economical.

[0035] W is added in order to increase a tensile strength at a hightemperature and hardness. W according to the present invention is usedin the range from 7.0 to 10.0 wt % against the total weight of thecomposition of the sintered alloy. When the content of W is less than7.0 wt %, a small quantity of carbide is formed so that a wearresistance becomes lowered. When the content of W is more than 10.0 wt%, the desired physical property is not increased any more.

[0036] Co used in the present invention is added in order to increasethe heat resistance and the hardness at a high temperature. Co is usedin the range from 2.0 to 3.5 wt % against the total weight of thecomposition of the sintered alloy. When the content of Co is less than2.0 wt %, a heat resistance effect is reduced. When the content of Co ismore than 3.5 wt %, increased performance is not economical.

[0037] Boron nitride used in the present invention is added in order toincrease a wear resistance. The boron nitride is used in the range from0.1 to 1.0 wt % against the total weight of the composition of thesintered alloy. When the content of the boron nitride is less than 0.1wt %, a wear resistance effect is reduced. When the content of the boronnitride is more than 1.0 wt %, the composition becomes weak.

[0038] Si used in the present invention is added as a de-oxidizer. Siprevents grain carbides from precipitating from grain boundaries duringmanufacturing process. Si plays a role for decreasing a grain oxidelayer. On the other hand, there is a trend that Si makes segregation inthe alloy, and also becomes a silicon oxide which exists in the steeland forms a grain oxide layer so that a content of Si has to be limited.In the present invention, Si is used in the range from 0.2 to 0.6 wt %,for example from 0.2 to 0.4%, against the total weight of thecomposition of the sintered alloy. When the content of Si is less than0.2 %, by weight, an effect of the de-oxidizer cannot be obtainedenough. When the content of Si is more than 0.6 wt %, it is notdesirable since a great deal of segregation is formed in the alloy.

[0039] Mn used in the present invention is added in order to combinewith a very small amount S(surfur) which may be present or be added toobtain MnS. Mn is used in the range from 0.2 to 0.5 wt % against thetotal weight of the composition of the sintered alloy. When the contentof Mn is less than 0.2 wt %, it is not desirable as it is difficult tohave a self-lubricity.

[0040] In a second step, the mixed metal powder is sintered.Advantageously, sintering is done at a temperature from about 1,140 toabout 1,180° C., preferably from 1,140 to 1,180° C., for example 1,160°C., for about 30 to about 50 minutes to form the sintered alloy. Thenthe sintered alloy product is cooled by air. When the sintering processis performed at lower than 1,140° C., the powder particles is notdispersed uniformly so that the base matrix becomes weaken. When thesintering process is performed at higher than 1,180° C., it is notdesirable since the grain increases in size so that a mechanicalproperty is deteriorated.

[0041] In a third step, the sub-zero treatment for the sintered alloy isperformed at a temperature from about −200 to about −160° C. for about 5to about 20 minutes. This sub-zero treatment favors a transformation ofthe alloy to reduce a residual austenite so that a mechanical propertyof the alloy can be improved. The inventors surprisingly found that thissub-zero treatment provides not only shortening of the prior preliminaryand main sintering processes for the sintered alloy, and but also thesintered alloy has superior physical property.

[0042] In fourth and fifth steps, An impregnating, lubricating metal,for example Pb, is impregnated into the sub-zero treated sintered alloyat a temperature from about 450° C. to about 550° C. for about 30 toabout 50 minutes and then the barrel process is performed at the sametemperature for about 80 to about 100 minutes.

[0043] Pb provides the self-lubricity to the lead-impregnated sinteredalloy composition and thus, it is possible to use for dried atmospherefuel. Pb of the present invention is used in the range from 10.0 to 15.0wt % against the total weight of the composition of the sintered alloy.When the content of Pb is less than 10.0 wt %, a great deal of unfilledpores remain. If the content of Pb is more than 15.0 wt %, it is notdesirable since surplus Pb is precipitated on the surface afterimpregnating.

[0044] The sintered alloy has an excellent wear resistance for theautomotive valve manufactured through the processes described. This isthe result of a surface characteristic of the lead-impregnated sinteredalloy in which micro spherical particles are dispersed uniformly in abase matrix of what can be characterized as a “high speed steel”metallic powder. A metal powder of a high speed steel containing C, Cr,Mo, V and W increases a cutting ability (and wear resistance) andimprove a surface property. The excellent abrasion resistance when anabrasion of alloy is in process is in part due to the very small size ofthe separated carbide and other hard particles within the sinteredalloy.

[0045] Further, the alloy of the present invention has a continuationproperty since dispersed metallic powders are extremely fine and thepowders having a lower hardness are mixed so that the workability can beenhanced during manufacturing process. The powders can be admixed in acontinuous process. Also, the alloy can renew itself as it is worn, asnew hard particles are subsequently exposed.

[0046] Advantageously the majority of the grains of the sinterable alloypowder comprise each of the metals in the alloy, most preferably withinthe prescribed concentration limits. In a less preferred embodiment,some or all grains do not comprise each of the metals in the alloy, butan aliquot of the well-mixed powder having many grains comprise each ofthe metals in the alloy, most preferably within the prescribedconcentration limits.

[0047] Additionally, valves and other items made from thelead-impregnated sintered alloy can be used for dried atmosphere fuelburning due to the self-lubricity obtained by the impregnation of Pb.

[0048] The present invention will be described in more detail taken inconjunction with the examples, however, the present invention is notlimited by the examples.

EXAMPLES 1-2 AND COMPARATIVE EXAMPLES 1-2

[0049] The sintered alloy for the valve seat is manufactured by mixingeach component and each content thereof are shown in Table 1. In eachcase, the mixed powder was formed under a pressure of 7 ton/cm³ and thenwas sintered at 1,170° C. for 40 minutes.

[0050] Then, for Examples 1 and 2, the sub-zero treatment was performedat a temperature of −180° C. for 10 minutes.

[0051] A tempering operation was then carried out for both the Examplesand the Comparative Examples at a temperature of 500° C. for 40 minutesafter impregnating Pb. Then, the barrel process is performed at atemperature of 430° C. for 90 minutes to manufacture the desiredlead-impregnated sintered alloy. The lead-impregnated sintered alloy ofComparative example was obtained by the same procedure of Example exceptskipping the sub-zero treatment.

[0052] [TESTING METHODS]

[0053] An amount abrasion from a pre-determined object made of thesintered alloy and having each component and each content as shown inTable 1, and manufactured by the process of the Example and comparativeexample, respectively, is measured and a result is shown in Table 1.

[0054] The Amount of abrasion test was performed by a simulation Rigtester wherein the CAM rotated at 2,500 rpm, the temperature was 400°C., the elapsed time was 10 hours, and the used fuel was LPG.

[0055] The result is the amount of the object that was abraded awayduring the 10 hour simulation Rig tester run. Compared with thecomparative example, an amount of abrasion of the sintered alloyaccording the example of the present invention is about 25 to 28% less,as shown in Table 1.

[0056] As mentioned above, according to the present invention, asintered alloy for an valve seat is modified by a sub-zero treatment fora metal power containing iron (Fe) as a main component, carbon (C),chromium (Cr), molybdenum (Mo), cobalt (Co), maganese (Mn), lead (Pb),vanadium (V), tungsten (W), optionally silicon (Si), and optionallysulfur (S), so that amount of metallic particles separated from a basematrix decreases and a size of the separated metallic particle becomessmall when an abrasion of the sintered alloy is in process, thereupon awear resistance and impact resistance are improved and a self-lubricityand a workability is enhanced. TABLE 1 Com. Com. Components Ex. 1 Ex. 2Ex. 1 Ex. 2 Composition C 1.4 1.4 0.8 0.8 (wt %) Cr 4 4 1 1 BN Mo 3 3 810 V 3.5 4 — — W 8.5 9 — — Si — — 0.5 0.5 Co 2.5 3 10 10 Mn 0.3 0.3 — —Pb 12 12 12 12 S 0.3 0.3 — — Boron 0.4 0.6 — — nitride Fe RemainderRemainder Remainder Remainder Abrasion amount(mm) 0.263 0.251 0.3570.345

[0057] Since corrosion resistance of the sintered alloy for a valve seatis improved according to the present invention by a sub-zero process, itis used for harsh conditions, for example in engines using smokelessgasoline and/or LPG under dried atmosphere.

[0058] While the present invention has been particularly shown anddescribed with reference to a particular embodiment thereof, it will beunderstood by those skilled in the art that various changes in form anddetail may be effected therein without departing from the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. An impregnated sintered alloy for use tomanufacture a valve seat, the impregnated sintered alloy comprising: Feas a main component, C of from 1.2 to 1.7 wt %, Cr of 3.5 to 5.0 wt %,Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0 wt %, W of 7.0 to 10.0 wt %, Coof 2.0 to 3.5 wt %, boron nitride of 0.1 to 1.0 wt %, S of 0.2 to 0.4 wt%, Mn of 0.2 to 0.5 wt %, and Pb of 10.0 to 15.0 wt %.
 2. Theimpregnated sintered alloy of claim 1 wherein the impregnated sinteredalloy consists essentially of Fe, C, Cr, Mo, V, W, Co, boron nitride, S,Mn, and Pb.
 3. The impregnated sintered alloy of claim 1 furthercomprising Si of from 0.2 to 0.6 wt %.
 4. The impregnated sintered alloyof claim 3 wherein the impregnated sintered alloy consists essentiallyof Fe, C, Cr, Mo, V, W, Co, boron nitride, S, Mn, Si, and Pb.
 5. Amethod for manufacturing a sintered alloy with excellent wear resistancefor a valve comprising: mixing Fe as a main component, C of from 1.2 to1.7 wt %, Cr of 3.5 to 5.0 wt %, Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0wt %, W of 7.0 to 10.0 wt %, Co of 2.0 to 3.5 wt %, boron nitride of 0.1to 1.0 wt %, S of 0.2 to 0.4 wt %, Mn of 0.2 to 0.5 wt %, and applying asurface pressure of 5 to 8 ton/cm³ to obtain a compressed mixed metalpowder; sintering the compressed mixed metal powder at a temperaturefrom 1,140° C. to 1,180° C. to form a sintered alloy and then cooling byair; performing a sub-zero treatment on the sintered metal powder at atemperature from −200 to −160° C.; impregnating the sub-zero-treatedsintered metal powder with Pb at a temperature from 450 to 550° C. toform an impregnated sintered alloy comprising from 10.0 to 15.0 wt % ofPb; and performing a barrel process for the sintered metal powderimpregnated with the Pb at a temperature from 450 to 550° C.
 6. A valveseat for an automobile engine, the valve seat comprising an impregnatedsintered alloy comprising: A) between about 85 parts by weight and a 90parts by weight, based on 100 parts of impregnated sintered alloy, of asintered powder alloy comprising: Fe as a main component, 1.2 to 1.7 wt% of C, 3.5to5.0 wt % of Cr, 2.0 to4.0 wt % of Mo, 3.0 to 5.0 wt % of V,7.0 to 10.0 wt % of W, 2.0 to 3.5 wt % of Co, 0.1 to 1.0 wt % of boronnitride, 0.2 to 0.4 wt % of S, and 0.2 to 0.5 wt % of Mn, wherein thesintered powder alloy comprises porosity; and B) between about 10 to 15parts by weight of a impregnated metal that has penetrating andlubricating properties, wherein the impregnated metal resides in theporosity.
 7. The impregnated sintered alloy of claim 6 wherein theimpregnated sintered alloy consists essentially of Fe, C, Cr, Mo, V, W,Co, boron nitride, S, and Mn, and wherein the impregnated metalcomprises Pb.
 8. The impregnated sintered alloy of claim 6 furthercomprising from 0.2 to0.6wt % of Si.
 9. The impregnated sintered alloyof claim 8 wherein the impregnated sintered alloy consists essentiallyof Fe, C, Cr, Mo, V, W, Co, boron nitride, Si, S, and Mn, and whereinthe impregnated metal comprises Pb.
 10. The impregnated sintered alloyof claim 8 wherein the impregnated sintered alloy comprises at leastabout 63.9% of Fe and wherein the impregnated metal consists essentiallyof Pb.
 11. The impregnated sintered alloy of claim 8 wherein theimpregnated sintered alloy comprises at least about 63.9% of Fe.
 12. Theimpregnated sintered alloy of claim 6 wherein the sintered alloycomprises at least about 63.9% of Fe, and wherein the sintered alloy wassintered at a temperature between about 1,140 to about 1,180° C., andthen cooled to a temperature of from about −200° C. to about −160° C.for a time sufficient to reduce the residual austenite in the sinteredalloy.
 13. The impregnated sintered alloy of claim 9 wherein thesintered alloy comprises at least about 63.9% of Fe, and wherein thesintered alloy was sintered at a temperature between about 1,140 toabout 1,180° C., and then cooled to a temperature of from about −200° C.to about −160° C. for a time sufficient to reduce the residual austenitein the sintered alloy.
 14. The impregnated sintered alloy of claim 13wherein the sintered alloy was held at a temperature of from about −200°C. to about −160° C. for about 5 to about 20 minutes.
 15. Theimpregnated sintered alloy of claim 6 wherein at least about 63.9% ofFe; about 1.4% of C is present in the sintered metal; about 4% of Cr ispresent in the sintered metal; about 3% of Mo is present in the sinteredmetal; about 3.5% to about 4% of V is present in the sintered metal;about 8.5% to about 9% of W is present in the sintered metal; about 2.5%to about 3% of Co is present in the sintered metal; about 0.4% to about0.6% of boron nitride is present in the sintered metal; 0.2 to 0.4 wt %of S is present in the sintered metal; about 0.3% of Mn is present inthe sintered metal; and wherein the impregnated metal consistsessentially of lead.
 16. The impregnated sintered alloy of claim 15wherein the sintered alloy comprises about 0.4% of Si, and wherein thesintered alloy was sintered at a temperature between about 1,140 toabout 1,180° C., and then cooled to a temperature of from about −200° C.to about −160° C. for a time sufficient to reduce the residual austenitein the sintered alloy.
 17. A method for manufacturing an engine valvecomprising: providing a sinterable alloy powder, wherein the sinterablealloy powder consists essentially of Fe as the main component; 1.2 to1.7 wt % of C; 3.5 to 5.0 wt % of Cr; 2 to 4 wt % of Mo; 3 to 5 wt % ofV; 7 to 10 wt % of W; 2 to 3.5 wt % of Co; 0.1 to 1.0 wt % of boronnitride; 0.2 to 0.4 wt % of S; and 0.2 to 0.5 wt % of Mn, wherein thesinterable alloy powder is in a mold; applying a surface pressure of 5to 8 ton/cm³ on the powder to obtain a compressed alloy powder havingporosity; sintering the compressed alloy powder at a temperature from1,140° C. to 1,180° C. to form a sintered alloy; cooling the sinteredalloy to a temperature of from −200 to −160° C. for at least about 5minutes, thereby forming a treated sintered alloy; heating the treatedsintered alloy to a temperature from about 450 to about 550° C. andimpregnating the treated sintered alloy with a penetrating metalcomprising Pb; thereby forming an impregnated treated sintered alloywherein the penetrating metal is present in the porosity in an amountbetween 10 to 15 wt % of penetrating metal; and performing a barrelprocess on the impregnated treated sintered alloy.
 18. The method ofclaim 17 wherein the sintered alloy further comprises 0.2 to 0.6% of Si.19. The method of claim 17 wherein a least a portion of the sinterablealloy powder grains comprise Fe as the main component; C; Cr; Mo; V; W;Co; boron nitride; and Mn.
 20. The method of claim 18 whereinsubstantially all of the sinterable alloy powder grains comprise Fe asthe main component; C; Cr; Mo; V; W; Co; boron nitride; and Mn.